Light emitting diodes (LEDs) enjoy widespread use in modern electronic devices. They are capable of emitting high-power light and offer more efficient power consumption, higher reliability, greater durability, and longer life, as compared to their conventional counterparts, including fluorescent lamps, incandescent bulbs, and halogen lamps. In addition, owing to their relatively small size, they can be configured in relatively small form factors.
In a conventional LED, a forward bias is applied to a p-n junction, causing holes in the p-type semiconductor material to recombine with electrons in the n-type semiconductor material. As a result of the recombination, optical energy is emitted at a wavelength that corresponds to the bandgap of the p-n junction.
For many LED applications, it is commonly desired to generate white light. There are a number of approaches for accomplishing this. In one approach, LEDs that generate red, green, and blue light, or LEDs that generate blue and yellow light, are combined in a single package to generate white light. This approach can lead to bulky packaging and complicated manufacturing procedures, since it requires the formation, electrical connection, and packaging of multiple LEDs in a fixed area.
In another approach, the output of a blue LED is made to be incident on a yellow phosphorescent material to generate a white output light as a result of the phosphorescent reaction. Alternatively, the output of an ultraviolet LED is made to be incident on a phosphorescent material including red, green and blue phosphorescent particles to generate a white output light as a result of the phosphorescent reaction. In these approaches, it can be difficult to control the quality of the white output light, since it depends highly on the concentration of the phosphorescent material. For example, in conventional approaches, the phosphorescent material is commonly mixed into a resin material that encases the LED in the package. This approach suffers from low color repeatability and therefore low reliability, since it is difficult to control the concentration of the phosphorescent material once it is mixed with the resin carrier.